Implantable medical devices (IMDs) are designed to work inside a human (or mammal), and are generally used for diagnosing, monitoring and treating diseases and disabilities. When requiring electrical power to operate, these devices are sometimes referred to as active. Today, as we continue to learn more about disease, new and increasingly sophisticated active IMDs are being developed, and our ability to meet the power and energy demands of these devices is becoming increasingly challenging.
Use of and demand for active IMDs is growing at an astounding rate. At the time of this writing applications abound: including, cardiac pacing; defibrillation; pain management; bone growth/repair; and treatment of a variety of maladies including movement and psychological disorders (including Parkinson's disease and epilepsy), scoliosis, hearing/deafness, vision/blindness, incontinence, gastroparesis, sexual dysfunction, cancer, and obesity; and the monitoring of diseases, generally via implantable sensors or detectors (e.g., monitoring cancer and diabetes); and fluid delivery of medicaments. It is clear just from this listing that the breadth of new implantable medical device applications will continue to expand well into the future.
The batteries that provide power to active IMDs are most often determinant of its service life. Indeed, it can be argued that the viability of a power hungry IMD, or that for which long service life is paramount, is linked to advances in battery technology, and in particular to that of lithium batteries, which, today, are the main energy sources in virtually every active IMD. For instance, the service life of the Li/I battery, the established power source of cardiac pacers for the last 30 years, is presently limiting pacemaker performance now that patient life expectancy is beyond 10 years from the date of implant.
The critical link between the success of an IMD and the battery that energizes it is no better exemplified than in the evolution of the cardiac pacemaker, still today the most commonly implanted active IMD Cardiac pacers, which deliver electrical pulses to a patient's heart so that it will beat at a desired rate, were first implanted successfully in the 1960s when they were powered by an implanted zinc/mercuric oxide battery, considered, at that time, to be the industry standard. However, those early pacemakers all suffered from leaks and short service life, the battery lasting, at best, about 2 years, and more typically less than that. Over time major breakthroughs have led to the development of the present day pacemaker. These include: i) hermetic casings and sealing technology, which have enabled significant improvements in patient compliance and device reliability; ii) low impedance electrodes and low power IC circuits, which in turn have led to such dramatic reductions in power requirements that the modern pacemaker is, today, a low power device; iii) the advent of microprocessors and the use of telemetry has enabled smart implantable devices communicable to an external operator; and iv) the innovation of the Li/I battery by Wilson Greatbach provided a dramatic increase in device longevity and reliability, and fostered along with it the era of the modern day pacemaker. When first introduced in about 1972 the Li/I battery provided key advantages over the state of the art, including: enhanced longevity, reliability and end of life predictable, all of which were critical to the eventual long term success of the pacer itself.
Presently more than 300,000 pacemakers are implanted in the United States annually and over 3 million are currently implanted in humans worldwide. Most, if not all, are powered by Li/I batteries. However, with increasing functionality and improvements in the safety of surgical implantations as well as longer patient life expectancy, pacemaker device longevity issues are back at the forefront, and along with that, there is again a need, if not a demand, for a longer lasting implantable power/energy source.
Indeed, the top reason for surgical removal of an active IMD is the need to replace the power source. Change out (i.e., replacing) of an implanted battery, or an entire IMD, can be exceptionally problematic, and is always associated with the inherent risk of infection. Patient preference, not unexpectedly, is almost always to remove that risk. Studies have shown that there is a nearly 7% chance of infection when an IMD is changed out, and this brings with it the possibility of mortality or complications thereafter.
Today there is a mismatch between patient longevity and active IMD service life. The present invention addresses this mismatch at the power/energy source level.